DIY Purifi Amp builds

[NTSOS]

Can you post a picture of the active LEDs you described? We might be misinterpreting your request. If you are not saying something is wrong, if you are just asking what to check before connecting speakers, then:
1. With open inputs and power on, use a voltmeter to check the output voltages (red to black) of each channel to confirm they are <50mV DC, and <10 mV AC.
2. If those are good, then power off, connect inputs, power on, play some music, and confirm that the AC voltage readings are now 'something', fluctuating.
3. Turn volume up. AC voltages should go up.
4. All good? Play on!

Yes, I'm just asking what to check before connecting speakers:

BTW, I only have the amp, no speakers, nothing.

If I'm doing this correctly, this is what I get:

Left - 19 mV AC
Right - 19 mV AC

Left - 6.0 mV DC
Right - 6.3 mV DC

 

[JimB]

Yes, I'm just asking what to check before connecting speakers:

BTW, I only have the amp, no speakers, nothing.

If I'm doing this correctly, this is what I get:

Left - 19 mV AC
Right - 19 mV AC

Left - 6.0 mV DC
Right - 6.3 mV DC

Okay. Move on to tests 2 and 3.

 

[NTSOS]

Okay. Move on to tests 2 and 3.

I wish I could.....I have no speakers.......everything has slowed due to covid 19. Whilst I'm waiting are the preliminary measurements I gave you ok?

Thanks Jim.

 

[JimB]

I wish I could.....I have no speakers.......everything has slowed due to covid 19. Whilst I'm waiting are the preliminary measurements I gave you ok?

Thanks Jim.

Yes. Your numbers are within limits of concern. My tests 2 and 3 do not involve speakers - they involve input signals and voltmeter observations on the outputs.

 

[NTSOS]

Yes. Your numbers are within limits of concern. My tests 2 and 3 do not involve speakers - they involve input signals and voltmeter observations on the outputs.

Oh, ok......got it, I have to read more carefully. I'll run the tests on Thursday as I have to wait for two XLR cables. Great, thanks!

Update:

I just received a response from Purify....I asked about a test procedure and their only response:

"If you have two red leds you are ready to play....just be sure to check the jumpers for unregulated supply".

I will still run your measurements on Thursday.

John

 

[NTSOS]

Yes. Your numbers are within limits of concern. My tests 2 and 3 do not involve speakers - they involve input signals and voltmeter observations on the outputs.

Hi Jim,

I ran test 2 and the AC voltages definitely fluctuate.

I ran test 3 and had to change the AC scale as the volume increased....it all seems to work.

Anything else I need to check?

Thanks.

John

 

[JimB]

Hi Jim,

I ran test 2 and the AC voltages definitely fluctuate.

I ran test 3 and had to change the AC scale as the volume increased....it all seems to work.

Anything else I need to check?

Thanks.

John

Sure - how does it sound?

 

[NTSOS]

Sure - how does it sound?

Yes, I wonder what it will sound like!

In any case, at least I can finish the chassis now with the knowledge that the amp works.

Thanks!

John

 

[JimB]

I'm very pleased to have just received my first EVAL1 Ghent cases - 3PM Christmas Eve! Mine are a bit different from those others have had. Mine have rear panels with only binding posts, which I had upgraded from their standard gold-plated brass to gold-plated copper. I expect this variant will be on the Ghent website soon, so I can share a few first observations. First, it looks good! I'll post specific considerations (pros and cons) for others a bit later.

 

[AndrewDavis]

When driving sensitive speakers, is there any sonic advantage for bypassing the buffer gain if the extra volume isn’t necessary? I’m driving Dynaudio M30s with the Eval 1 stereo 1ET400A amp and a RME ADI-2 and I rarely get past -30db volume.

 

[JimB]

When driving sensitive speakers, is there any sonic advantage for bypassing the buffer gain if the extra volume isn’t necessary? I’m driving Dynaudio M30s with the Eval 1 stereo 1ET400A amp and a RME ADI-2 and I rarely get past -30db volume.

Technically, yes, IF your source can drive it. Sonically? Maybe not in most cases.

 

[JimB]

I'm very pleased to have just received my first EVAL1 Ghent cases - 3PM Christmas Eve! Mine are a bit different from those others have had. Mine have rear panels with only binding posts, which I had upgraded from their standard gold-plated brass to gold-plated copper. I expect this variant will be on the Ghent website soon, so I can share a few first observations. First, it looks good! I'll post specific considerations (pros and cons) for others a bit later.

First, note that you MUST modify your EVAL1 FE02 board to use this back panel - you must at least remove the plastic lips of the DELTRON-style sockets, and the handle of the S1 switch, as I have described before. https://www.audiosciencereview.com/...y-purifi-amp-builds.10478/page-25#post-344897

In my picture, I removed the sockets and switch, but this is not necessary, mechanically. However, if you will want to take the feedback sense point from the binding posts, you will have to remove the DELTRON-style sockets. https://www.audiosciencereview.com/...y-purifi-amp-builds.10478/page-25#post-344882

I had a surprise when the kit came with a fused, filtered mains switch/socket! Those who like a back panel fuse should be pleased. Mine are fitted with 10A (fast blow?) fuses, which suit me with 120VAC mains. @wineds would approve. I haven't evaluated the values of the filter, so I don't know how useful it is. I note that it is rated for 10A, which is a bit low for a 1200W SMPS, but not out of the question as one will not run the amp at 1200W, continuously - ever.

EDIT. Update here: https://www.audiosciencereview.com/...y-purifi-amp-builds.10478/page-98#post-617372

Another surprise was that it doesn't quite fit the panel - it's a touch taller than the panel hole. Ghent will have to adjust hole size in a future run. I suspect I'll just file the edges of the plastic to get a fit, rather than wait for replacements.

My binding posts came with "key washers" in random orientations, such that locking them into the keyed panel holes put the solder cup of some up, and others down. I prefer the cup to be open on top, so I had to pry the keyed washers out to rotate them to assemble the posts as I wanted. On the left is my "wrong" orientation and the right is "right".

Others have commented about lack of screws in their kits. Mine seems complete, but the small, black flat-head screws that one would use to secure the XLR sockets to the back panel are machine screws, rather than self tapping. They don't work well.

I'd recommend finding some M3x8 (or x10 or x12), self tapping screws. It turns out that there were usable screws in two of the three case kits I received - I just happened to have started with the one that did not have any. For reference, this is the official Neutrik Plastite screw (E-SCREW1-12B):

EDIT. Updates here: https://www.audiosciencereview.com/...y-purifi-amp-builds.10478/page-96#post-614091

 

[NTSOS]

I'm very pleased to have just received my first EVAL1 Ghent cases - 3PM Christmas Eve! Mine are a bit different from those others have had. Mine have rear panels with only binding posts, which I had upgraded from their standard gold-plated brass to gold-plated copper. I expect this variant will be on the Ghent website soon, so I can share a few first observations. First, it looks good! I'll post specific considerations (pros and cons) for others a bit later.
View attachment 101409

View attachment 101410

Hi Jim....why are the Delrons being removed by many people for their builds? Is it because they are not structurally supported very well, Ghent doesn't make a back plate to fit or are there other reasons....just curious?

 

[JimB]

Hi Jim....why are the Delrons being removed by many people for their builds? Is it because they are not structurally supported very well, Ghent doesn't make a back plate to fit or are there other reasons....just curious?

I don't know that any people are removing their DELRONs, so can't address that. There is nothing 'wrong' with the DELRONs, in my opinion! Certainly Ghent has a case that uses them. It was the first they offered and it is a 'combo' case that adds speakONs.
http://www.ghentaudio.com/kit/purifi-eval1-se.html

I have no use for both DELRONs, which only take banana plugs, AND the binding posts I wanted, which take banana plugs, wire and spades. To use the new Ghent case, without holes for the DELRONs, you only need to clip off the faces of the DELRONs, not remove them. You can solder wires up from the board to the sockets, as people do with the combo Ghent case. But I want to use connector feedback, so I need to remove the DELRONs to disconnect the feedback path through them on the board. These topics were discussed long ago in this topic if you'd like to read more.

 

[NTSOS]

I don't know that any people are removing their DELRONs, so can't address that. There is nothing 'wrong' with the DELRONs, in my opinion! Certainly Ghent has a case that uses them. It was the first they offered and it is a 'combo' case that adds speakONs.
http://www.ghentaudio.com/kit/purifi-eval1-se.html

I have no use for both DELRONs, which only take banana plugs, AND the binding posts I wanted, which take banana plugs, wire and spades. To use the new Ghent case, without holes for the DELRONs, you only need to clip off the faces of the DELRONs, not remove them. You can solder wires up from the board to the sockets, as people do with the combo Ghent case. But I want to use connector feedback, so I need to remove the DELRONs to disconnect the feedback path through them on the board. These topics were discussed long ago in this topic if you'd like to read more.

Ok, thank you!

 

[JimB]

... I had a surprise when the kit came with a fused, filtered mains switch/socket! Those who like a back panel fuse should be pleased. Mine are fitted with 10A (fast blow?) fuses, which suit me with 120VAC mains. @wineds would approve. I haven't evaluated the values of the filter, so I don't know how useful it is. I note that it is rated for 10A, which is a bit low for a 1200W SMPS, but not out of the question as one will not run the amp at 1200W, continuously - ever.

Another surprise was that it doesn't quite fit the panel - it's a touch taller than the panel hole. Ghent will have to adjust hole size in a future run. I suspect I'll just file the edges of the plastic to get a fit, rather than wait for replacements.
View attachment 101425

Others have commented about lack of screws in their kits. Mine seems complete, but the small, black flat-head screws that one would use to secure the XLR sockets to the back panel are machine screws, rather than self tapping. They don't work well.

I'd recommend finding some M3x8, self tapping screws.

I've now heard back from Ghent. They suggested the filtered mains socket be mounted on the outside of the panel, and, indeed, it fits fine that way, through I prefer the cosmetics of it internally. It does just clear the panel labeling - it is blocked in this photo due to camera distance.

They also confirm that self tapping screws for the XLRs should be included (my shipment was custom, and rushed for the holiday). I'll be special ordering some of these: https://www.mouser.com/ProductDetail/Neutrik/E-SCREW1-12-B/?qs=b0EQgHdmdbkpPIHTS6VUSQ==

 

[TimoJ]

I recall a recommendation not to use filtered AC input in D-class amps. Was it on Hypex documents?

 

[AndrewDavis]

I've now heard back from Ghent. They suggested the filtered mains socket be mounted on the outside of the panel, and, indeed, it fits fine that way, through I prefer the cosmetics of it internally. It does just clear the panel labeling - it is blocked in this photo due to camera distance.
View attachment 101500

They also confirm that self tapping screws for the XLRs should be included (my shipment was custom, and rushed for the holiday). I'll be special ordering some of these: https://www.mouser.com/ProductDetail/Neutrik/E-SCREW1-12-B/?qs=b0EQgHdmdbkpPIHTS6VUSQ==

My case kit also did not have those screws. I asked Ghent for recommendations on buying screws amd they just sent me some. 5 small screws, halfway across the globe.

 

[barrows]

I recall a recommendation not to use filtered AC input in D-class amps. Was it on Hypex documents?

The reason for this is that the SMPS commonly used (SMPS 1200) already have extensive input filtering, and adding additional filtering can create a resonance problem, creating more noise at the input to the power supply than without adding such additional filtering. Unless you can specifically test an input filter when used with the SMPS 1200 for resonances, you should not add additional filtering to the AC input. These kind of filter circuits need to be properly tuned, and should not be applied indiscriminately.

BTW, has anyone considered trying OPA 1622 in a Purifi amplifier input buffer? There are DIP 8 modules available using this OPA from Audiophonics. The part is interesting to me because of its high current capability. The DIP 8 modules should be able to drop into any input buffer board which is socketed, like Nord, and Apollon, etc.

 

[March Audio]

The reason for this is that the SMPS commonly used (SMPS 1200) already have extensive input filtering, and adding additional filtering can create a resonance problem, creating more noise at the input to the power supply than without adding such additional filtering. Unless you can specifically test an input filter when used with the SMPS 1200 for resonances, you should not add additional filtering to the AC input. These kind of filter circuits need to be properly tuned, and should not be applied indiscriminately.

BTW, has anyone considered trying OPA 1622 in a Purifi amplifier input buffer? There are DIP 8 modules available using this OPA from Audiophonics. The part is interesting to me because of its high current capability. The DIP 8 modules should be bale to drop into any input buffer board which is socketed, like Nord, and Apollon, etc.

The designer Bruno Putzeys comments on mains filters:

https://www.diyaudio.com/forums/class-d/38199-ucd180-questions-post466003.html

Do not use mains filters with Y capacitors installed. An Y capacitor makes a capacitive connection (several nf) from the mains lines to your chassis and hence audio ground.

So there is the audiophile designer, using transformers with a shield to remove the slightest chance of the mains polluting his system ground, then installing a schaffner inlet that puts 2.2nF straight from the mains into the chassis, simply because he heard somewhere that mains disturbances are audible. They are, more precisely when such a filter is used.

All commercially available "combined mains filters" have Y capacitors. Don't use them. If all your audio devices are connected to one wall outlet (likely), you can use such a filter there, but by no means on individual boxes.

In principle you could make a filter with only chokes (cm/dm) and an X capacitor. Fine with me, but unless you have a problem with heavily polluted mains you don't need them.
The UcD will not be a source of mains pollution. If your mains are polluted by an external cause (like you have a car factory next door), a centralised filter on the outlet is more effective.

Fyi, none of my audio devices have mains filters on them